A carbon fiber-reinforced carbon composite (hereinafter referred to as "C/C composite") is a very light material such that its specific gravity is as low as 1.5-1.7 and can retain high strength of the order of more than 1,000 kg f/cm.sup.2 at high temperatures of more than 1,500.degree. C. It is expected, therefore, that use of such composite will steadily grow in various high technology applications.
In space navigation, for example, it is well anticipated that a space shuttle will be exposed to considerable pressre under high temperature conditions of more than 1,700.degree. C. when it dives at superhigh speed from the outer space into the atmosphere. For use under such demanding conditions, C/C composites are most highly recommended. However, C/C composites are comprised of carbon material only and will be oxidized and consumed at temperatures of more than 400.degree. C., in an oxidizing atmosphere as in the air. As such, areas of their applicability are limited.
In order to improve the oxidation resistance of C/C composites, attempts have been made to cover the C/C composite with SiC by chemical vapor deposition (CVD). However, because of the fact that the linear expansion coefficient of SiC is widely different from that of C/C composite, the former being 4.5.times.10.sup.-6 whereas the latter is 1.5.times.10.sup.-6, even if SiC is uniformly deposited on the C/C composite by CVD at about 1,500.degree. C., fine cracks will develop when the temperature is lowered to room temperature, with the result that the carbon goes in contact with air through the cracks to become oxidized. In order to prevent the occurrence of such trouble, the C/C composite may be first covered with B.sub.2 O.sub.3 or TiC and then with SiC so that the resulting composite material has stepwise varied linear expansion coefficients, it being thus possible to prevent cracking due to temperature changes. However, this method is yet unsatisfactory to solve the problem and, in addition, it requires a complicated and costly process for fabrication. Further, an oxidation resistant layer formed in such a way is disadvantageous in that it is of relatively low strength and is liable to cracking when considerable force and heat is applied to the surface of the compsite material as in the case where a space shuttle dives at superhigh speed into the atmosphere, so that oxidation occurs through the crack which will finally result in peeling off of the layer, considerable loss of strength of the C/C composite, and loss of its heat resisting properties.